This invention relates to a metal gasket and particularly relates to a metal gasket provided with a bead or beads.
Recently, a requirement for a gasket has become severe in association with enhancement of performance in a modem internal combustion engine. The gasket is required to be thinner in thickness and higher in gas-sealing function to cope with a higher inner pressure in engines.
In reply to the requirement, a metal gasket has been proposed which uses a thin metal plate in which a sealing line with a greater surface pressure is provided around an opening therein by effecting a grommet working, a seam welding, or a bead forming, or by attachment of a resilient seal member in order to assure a gas-sealing function.
However, a metal gasket, on which a grommet is welded, can have a sealing line only a limited position such as a periphery of the opening, cannot support the grommet on account of lack of a sealing width in the case where a flange is narrow, and cannot have a quantity of step difference less than a thickness of the grommet since the quantity of step difference is determined by the thickness of the grommet. On the other hand, although a metal gasket with beads can be advantageously formed into a thin thickness, breakage of sealing will be readily caused due to a collapse of the bead, since a surface pressure to be exerted in the gasket is determined by a dimension and a shape of the bead. The metal gasket with the resilient seal member requires a design of the number and shape of the resilient seal member for every type of gasket since it is difficult to control a quantity of compression of the resilient seal member. This is troublesome. Such metal gasket is poor in durability since it is subject to a great secular change. Further, it is likely to lose a gas-sealing function due to separation upon mechanical vibrations.
Another metal gasket in which a resilient seal member is attached to a bead has been proposed in order to improve a property of fatigue resistance of the bead. Although such metal gasket can maintain a desired surface pressure on a convex surface of the bead, the gasket cannot assure a desired sealing surface pressure on a concave surface of the bead, since a fastening load on the concave surface of the bead is distributed on three positions, that is, the resilient seal member and a pair of standing portions of the bead.